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174 votes
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Why are IPv4 addresses running out?

The IPv4 Address Shortage According to Vint Cerf (the father of IP), the IPv4 32-bit address size of was chosen arbitrarily. IP was a government/academic collaborative experiment, and the current ...
Ron Maupin's user avatar
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40 votes
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What is the difference between 0.0.0.0 and a loopback IP address?

The statement: The IP address 0.0.0.0 [...] means ‘‘this network’’ or ‘‘this host.’’ is misleading. It is not a "or" but "This host on this network." From RFC1122: { 0, 0 } ...
JFL's user avatar
  • 19.7k
39 votes

Why are IPv4 addresses running out?

Ron Maupin's answer gives a brilliant overview of the IPv4 shortage, but I'd like to address this part of your question: Why can't a city (for example) have just one IP address and all homes in ...
IMSoP's user avatar
  • 490
33 votes
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Why are IP addresses given to each interface and not device? What would the implications of that be?

Connecting an interface to a network makes it a part of that network. Therefore, the IP address is a property of the connection, not the host. Likewise, a host can have many network connections and ...
Zac67's user avatar
  • 84.9k
33 votes
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What stops someone from configuring their network with IP addresses they do not own?

Most likely if they're a big university they are their own ISP, using BGP to connect their network to the internet via a number of upstream networks. Nothing stops them from using IP addresses they ...
Teun Vink's user avatar
  • 17.4k
28 votes

How do you calculate the prefix, network, subnet, and host numbers?

Part 1 of 2 IPv4 Math With an IPv4 address and the network mask, the network mask length, or host mask, you can calculate the Network Address, Broadcast Address, Total Addresses, Usable Addresses, ...
Ron Maupin's user avatar
  • 99.8k
22 votes

How do you calculate the prefix, network, subnet, and host numbers?

Continued from Part 1... Part 2 of 2 Subnet IPv4 Networks Subnetting a network is creating multiple, longer networks from a network address and mask. The basic idea is that you borrow high-order ...
Ron Maupin's user avatar
  • 99.8k
22 votes

Does every host on the LAN share the same ARP table, or do hosts keep them individually?

Actually, every interface in a device has its own ARP table. A host could have several ARP tables (one for each interface it has). ARP tables are not shared between hosts, or even among interfaces in ...
Ron Maupin's user avatar
  • 99.8k
22 votes

Difference between :: and ::1

:: is the unspecified address (0:0:0:0:0:0:0:0), and it is only used in packets as the source address of a host that does not yet have an address and is trying to get an address assigned. What you see ...
Ron Maupin's user avatar
  • 99.8k
21 votes

Is `0.0.0.0/1` a valid IP address? If so, what does it indicate?

Zac is muddying the waters by excluding 0.0.0.0/8 and 127.0.0.0/8. While addresses in those two prefixes should never appear on the wire, 0.0.0.0/1 does cover them. The slash notation works the same ...
Ricky's user avatar
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20 votes
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Does anycast addressing add additional latency in any way?

Does anycast addressing, in itself, add any additional latency to network connections? No. one using unicast and the other using anycast Anycast is unicast. It is just that the same network is ...
Ron Maupin's user avatar
  • 99.8k
19 votes
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Why are there 3 ranges of private IPv4 addresses?

Back when the RFC for private addressing was proposed, classful addressing was still common. The reasons for the three address ranges are found in RFC 1918, Address Allocation for Private Internets: ...
Ron Maupin's user avatar
  • 99.8k
19 votes
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IPv4 Segment 100.64.0.0/10

The 100.64.0.0/10 address block is not private address space; it is shared address space. This is spelled out in RFC 6598, IANA-Reserved IPv4 Prefix for Shared Address Space (I highlighted the ...
Ron Maupin's user avatar
  • 99.8k
19 votes
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What are common sizes to split a /29 - /32 IPv6 subnet?

Some simple guidelines that work most of the time: Dividing your /29 The standard size of your allocation from RIPE NCC is a /32 A /32 is a well-accepted prefix size in the global routing table You ...
Sander Steffann's user avatar
19 votes
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What happens when a subnet reaches capacity?

A subnet (network) is really just a collection of contiguous addresses within a binary mask. It is simply a logical way to divide address block. If you run out of addresses in a network (subnet), then ...
Ron Maupin's user avatar
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19 votes
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Is there anything stopping me from using Class A addresses on my own network?

As long as you are translating your "15.0.0.0" address space to something unique on the Internet that doesn't overlap, things will "work fine". However, you won't be able to ...
Eddie's user avatar
  • 15k
17 votes

Why are IP addresses given to each interface and not device? What would the implications of that be?

It would not be enough. Suppose I have a computer with three interfaces: eth0 (wired Ethernet), wlan0 (wifi), and vboxnet0 (virtualbox). One of the interfaces is connected to an internal network, one ...
Piskvor left the building's user avatar
17 votes
Accepted

Why the first octet of a MAC address always end with a binary 0?

You may notice that two least-significant bits of the most-significant byte of a 48-bit MAC address are usually set to 0 (as in all your examples). There are two flags in the most-significant byte of ...
Ron Maupin's user avatar
  • 99.8k
16 votes

Why do we need MAC Address if we can uniquely identify each machine with an IP Address

There is a historical reason for this, as @ronmaupin alludes to. In small networks, you don't need a layer 3 protocol. All the devices are directly addressable, so layer 2 addresses work fine. As ...
Ron Trunk's user avatar
  • 67.7k
16 votes

Why are IPv4 addresses running out?

Right now, every home has its own IP address. Why can't a city (for example) have just one IP address and all homes in this city would just be on a private network of that city? Exactly this is ...
Martin Rosenau's user avatar
16 votes
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Is `0.0.0.0/1` a valid IP address? If so, what does it indicate?

0.0.0.0 is no valid IP address, regardless of prefix length. 0.0.0.0/0 as prefix matches any address, so it's used for the default route. Also, 0.0.0.0 is the unspecified address used in many APIs, ...
Zac67's user avatar
  • 84.9k
14 votes
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How do routers on the backbone avoid IP address conflicts?

The RIRs assign addressing to the ISPs. An ISP not following the rules will quickly find itself ostracized and cut off from the rest of the Internet. IANA owns the addressing and assigns each of the ...
Ron Maupin's user avatar
  • 99.8k
14 votes

Why can I send 127.0.0.1 to 127.0.0.0 on my network?

we changed our FW so that the fixed IP addresses are 127.0.0.0 and 127.0.0.1. Generally, that's a really bad idea. It is in violation of RFC 1122: (g) { 127, <any> } ...
Zac67's user avatar
  • 84.9k
13 votes

What is the difference between 0.0.0.0 and a loopback IP address?

If I am correct, a loopback IP address refers to the current host. No. Traffic sent to a loopback address loops back inside the host. You can send traffic to a loopback address as the destination ...
Ron Maupin's user avatar
  • 99.8k
13 votes
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What are the negative impacts of using non RFC1918 addresses on a private network?

If those devices will actually never access the Internet, then the devices themselves will be fine, however there's still some potential issues: what about other system that must communicate with ...
JFL's user avatar
  • 19.7k
12 votes
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Which CIDR block contains the most IP addresses, 192.168.0.0/16 or 169.254.0.0/16?

These IP blocks contain exactly the same number of IP addresses. An IP is made of 4 bytes, separated by dots. Each byte can take (theorically) the value from 0 to 255, meaning 256 different values, ...
Sébastien VALSEMEY's user avatar
12 votes

What is Link-local addressing?

Link-local addresses are used for communication between two hosts (which are on the same link) when no other IP address is specified. In simple words, at the time of booting up, the OS tries to ...
Gaurav Kansal's user avatar
12 votes

Is there anything stopping me from using Class A addresses on my own network?

Any network addresses you use in your own company that are in use or assigned to a different company on the public Internet will be inaccessible to your users trying to reach those addresses on the ...
Ron Maupin's user avatar
  • 99.8k
12 votes
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What is the use-case of including the IPv4 address in IPv6 address?

There are some common use cases: ::ffff:192.168.0.1 This is used in software that uses IPv6 sockets even for handling IPv4 connections. That makes it easier to write software because everything ...
Sander Steffann's user avatar

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